Overload switch for motors



April 8, 1924.

F. TOBIEN OVERLOAD SWITCH FOR MOTORS Filed Deb. 29. 1921 Patented Apr. 8, 1924.

FELIX TQBIEN, F ESSEN, GERMANY,

ASSIGNOR TO FRIED. KRUPP AKTIEN- GESELLSCHAFT, 0F ESSEN-ON-THE-RUHR, GERMANY.

OVERLOAD SWITCH FOR MOTORS.

Application filed December 29, 1921.

To all whom it may concern.

Be it known that I, FELIX ToBInN, residing at Essen, Germany, a citizen of the German Republic, have'invented a certain new and useful Improvement in Overload Switches for Motors, of which the following is a specification.

This invention relates to overload switches for motors, which are started by means of a starting resistance.

The object of the inventionis to provide an overload switch, the sensitiveness of which automatically varies during'the starting and which, when used for the protection of motors which are connectible in seriesparallel relation, undergoes a variation when the connection is changed from series to parallel.

An embodiment of the invention is diagrammatically illustrated in the drawing, when the overload switch serves to protect two car motors connectible in series or in parallel.

Fig.1 showing the switch in operative position when the motors are in series, and

Fig. 2 showing the same when the motors are connected up in parallel.

To thecurrent collector B, running on the overhead conductor A, are connected in series, in the arrangement of Fig. 1, the main circuit breaker coil C and the circuit breaker, composed of two fixed contacts C and G and a movable contact C, of the overload switch, the starting resistance D with slide contact al and the two car motors E E and F F, provided with series fieldwindings. The field winding F of the second motor F F has one terminal connected to earth. With the coil C and the contacts C C connected withit in series, of the overload switch is connected in parallel a branch circuit which contains a magnet coil C acting in the same direction as the coil C, and a series resistance C. -The exciting force of said coil G which works on the same magnetic circuit as the coil C, is so proportioned that it cannot open the closed overload switch but tends to hold the opened switch against the force of a spring C, connected to the movable contact C. Another magnet coil C is connected through a resistance G on one side to earth and on the other side to the point of connection of the two motors.

This coil C also works in the same direction as the main circuit breaking coil C.

Serial No. 525,695.

The coil C and resistance Gare so proportioned that the coil C when the motors are running at full speed and the starting resistance D is consequently short-circuited, can furnish as great an exciting force as the main coil C.

In Fig. 2 the motors E E and F F are not connected in series but in parallel. The points of the circuit, to which the magnet coil C and the resistance G are connected, are connected together by a shunt wire H, so that they represent at this time points of equal potential. The slide contact (Z is in such a position, as in Fig. 1, that the starting resistance D is fully cut in.

When all the parts are in the position shown in Fig. 1, in which particularly the two inotors are connected in series, the overload switch is closed and, the slide contact (Z is so placed that the starting resistance D is fully cut in, then the magnet coil C receives no current, since the entire line potential is consumed (up to a practically neglible amount) in the starting resistance D. Consequently the only active coil is the circuit breaker coil C; so that the overload switch has only a slight sensitiveness. In proportion as the starting resistance D is being diminished, the portion of the line potential impressed upon the motor F F and therewith the number of revolutions of the motors increases, the current in the magnet coil C rises, so that the magnetic circuit of the overload switch becomes more and more strongly excited. But at the same time the sensitiveness of the overload switch increases, until it attains its highest value when the starting resistance is shortcircuited.

In changing to the parallel connection of the motors E E and F F (Fig. 2), the following connections are established by the controller switch (not shown) first the connection between the field winding E and the armature F is broken; secondly the armature E is connected with the armature F through a conductor J and the field winding E with the field winding F through the conductor H, and thirdly the slide contact al comes again into that position in which the start ing resistance D is fully cut in. The ends of the branch circuit, containing the magnet coil C and the resistance G, remain conductively connected with the field windings E and F Said branch circuit is therefore now short-circuited by the wire H. Conse p1entl3 in all positions. which the slide contact (Z can take the magnet coil C remains unexcited, so that the sensitiveness of the overload switch assumes the same alue as at the beginning 01 the starting when the motors E E and F F are connected in series.

lVithout in any way changing the int-ention, the two motors connectible in series and parallel could be replaced by a single motor and the strength of the exciting current he made dependent upon the tall oi? potential in said motor. In this case the resistance G can he so proportioned that the overload switch is twice as sensitive when the starting resistance is short-circuited, as when the latter is fully cut in.

Claims:

1. in electrical system of connections comprising an electrical translating device; a starting current-diminishingmeans tor the protection o't said translating devics and an electromagnetic overload switch comprising a main urrent cinitrol coil tending to open said switch a second coil operativel v connected across said. switch and adapted to retain said, switch in open condition. and a third coil operativelv connected to said translating device to increase the sensitiveness of said overload switch when the current-diminishing means is graduall eliminated.

l in electrical system of connections comprising an electrical translating device; a starting current-diminishing means for the protection of said. translating device and an electromagnetic overload switch comprising a main current control coil tending to open said switch. a second coil operativelv connected to said switch in series with a re sistanci and a daptcd to retain said switch in open condition. and a third coil operativel connected to said translating device to increase the sensitivencss of said overload switch when the current-diminishing .11 ans is gradmdlv eliminated.

3. An electrical system of connections comln'ising a number of electrical motors; a starting current-diminishing means for the protection of said motors and an electromagnetic overload switch comprising a main urrent control coiltending to open said switch a second coil operatively connected to said switch and adapted to retain said switch in open condition, and a. third coil operatively connected to one of said motors to increase the sensitiveness of said overload switch when the current-diminishing means is gradually eliminated.

4:. An electrical system of connections comprising an electrical translating device; a. starting currcnt-controlling means for the protection of said translating device and an electromagnetic overload switch comprising a main current control coil tending to open said switch. a second coil operativelv connected to said switch and adapted to retain said switch in open condition. and a third coil normally shunted across said translating device to increase the sensitiveness of said overload switch when the current-cmitrolling means is gradually eliminated.

5. An electrical system ot connections comprising an electrical translating device; a starting current-controlling means for the protection of said translating device and an electromagnetic overload switch comprising a main current control coil tending to open said switch, a second coil operatively connected to said switch in series with a resistance and adapted to retain said switch in open condition and a third coil connected in series with another resistance and normally shunted across said translating device to increase the sensitiveness of said overload switch when the current-controlling means is gradually eliminated.

6. An electrical system of connections comprising two electric motors; a starting current-controlling means tor the protection of said motors and an electromagnetic overload switch comprising a main current control coil tending to open said switch and an auxiliary control coil normall connected in shunt with one of said motors when the mo tors are in series but short circuitcd when the motors are in parallel.

7. An electrical system of connections cinnprising two electric motors; a starting cm'rent-controlling means for the protection of said motors and an elcctro-magnetie oven load switch comprising a main current control coil tending to open said switch, a second coil operativelv connected to saidswitch and adapted to retain said switch in open position, and an auxiliary control coil normally connected in shunt with one of said motors when the motors are in series hut short-circuited when the motors are in parallel.

The foregoing specification signed at: Essen. rermany, this 28th da v of November, 1921.

F15 LIX 'l. 015 IF X 

